High pressure valves with synthetic sealing elements, in particular plastomers as e.g. polyamides (Nylon®)), polychlorotrifluoroethylenes (KEL-F®), polyurethanes or polyetheretherketones, are well known in the art. They provide a far better sealing result than high pressure valves with metallic sealing elements. However, when valves are to be used in oxygen circuits with high flow rates and high gas pressures (as e.g. in oxygen cylinder filling stations), synthetic sealing elements have to be avoided. The reason for avoiding synthetic materials in valves for such applications is the risk of ignition due to adiabatic compression shocks. Rapid and important flow rate increases in a high pressure oxygen circuit—which may e.g. be due to the quick opening of a valve in the circuit—result in an adiabatic compression of the oxygen in the seat area of the valve, which will be accompanied by an important heat generation. Such adiabatic compression shocks can result in temperature peaks that do by far exceed the ignition temperature of known synthetic sealing materials. Once ignition of the synthetic sealing element has started in the oxygen flux, it will quickly spread and will in most cases result in a so called oxygen burnout of the valve. Such an oxygen burnout of the valve does not only destroy the valve, it may also result in fire and explosions.
The risk of important adiabatic compression shocks in the valve—and consequently the risk of oxygen burnout of the valve—increases with gas pressure. Therefore, oxygen valves to be used for pressures above 200 bars have nowadays exclusively metallic sealing elements. However, high pressure valves with metallic sealing elements provide less good sealing results than high pressure valves with synthetic sealing elements.